The present invention relates to an elastic shaft coupling comprising at least one torsion element having at least one elastomer body serving as a transmission element. Axial metallic connecting flanges are mounted in a fixed manner on said elastomer body on the input and output sides particularly by vulcanization
In conjunction with such shaft couplings comprising torsion elements, the torque is exclusively transmitted via one or a plurality of elastomer bodies, which, as a rule, are high-quality coupling rubber bodies. Metallic connecting flanges in the form of disks are undetachably mounted on the axial face sides of the one or more rubber bodies for introducing the torque into said rubber body or bodies. The best joint is currently produced by vulcanization.
Under dynamic load, i.e. in the transmission of torques that are variable in terms of time, as they are present, for example due to torque peaks in large diesel engines with low flywheel mass, the transmission elements are subjected to torsion that is variable in terms of time as well. Due to such dynamic load, heat loss occurs in the course of deformation of the elastomer body as a result of internal friction. Since the stressability of elastomer materials even with the highest operational efficiency decreases with the rise in temperature, efficient measures are employed for cooling, i.e. for dissipating heat from the rubber body.
For cooling the core areas of the rubber bodies, which require special attention in light of the fact that elastomer materials basically have a relatively low specific thermal conductivity, it is already known since a long time to employ instead of a ring-shaped, through-extending elastomer transmission element a plurality of segment-shaped torsion elements having connecting flange segments. Such a torsion element is known, for example from DE 37 10 390 C2.
It is also known already from said DE 7 10 390 C2 to provide both one-piece, ring-shaped and segment-shaped torsion elements with axial breakthroughs extending axially through the connecting flanges, and the elastomer body with axial venting channels.
The cooling air, which flows in between the segments or through the breakthroughs in the connecting flanges, provides in an advantageous manner for effective air cooling of the rubber bodies, so that it was possible to substantially increase the power density of such torsion elements. This, however, leads to particularly high loads acting on the elastomer/metal joint, i.e. the active vulcanized area of the rubber body on the connecting flange. Particularly endangered with respect to the formation of cracks in the rubber, or initial tearing of the elastomer/metal joint, are the edges of the connection area on the radial outer edges of the connection flange segments, or on the inner edges of breakthroughs, i.e. of venting openings in the connecting flanges.
For the purpose of preventing the formation of cracks and detachment in the marginal zones or on the edges of the rubber/metal joint, it has already been proposed in AT 154 034 to round off the edges and to design the rubber body in such a way that it extends around the face sides of the edges. A further development of said basic idea is specified in DE 33 10 695 C2. Said document relates to torsion elements where the radial face edges of the connecting flange segments are provided with a rounded-off profiling, around which the rubber body is drawn.
The measures according to the prior.art explained above offer the advantage that the adhesion of the rubber body to the edge of the rubber/metal connection area is enhanced. Another positive effect is that the axial width of the rubber body in said marginal zones and thus the active elastic length are increased. However, in light of the fact that the requirements that have to be satisfied with respect to power density are constantly increasing, the limits of the measures specified above have just about been reached in the meantime, because it has been found that under maximum load, bending stresses are exerted on the projecting area of the rubber body in spite of the curved profiling of the edges. Furthermore, the active elastic length within the zone of the radial faces of the segments or in the cross section of the breakthroughs in the connecting flange can be increased only by the axial thickness of the material of the connecting flanges. This defines stress limits which, until the present time, cannot be exceeded.
Now, the problem on which the present invention is based is to further develop torsion elements of the type specified above in that higher transmittable power densities become possible. Such optimization takes into account particularly the special stress occurring within the area of the faces of connection flange segments and along the edges of the breakthroughs in the connecting flanges.
For solving said problem, the invention proposes that at least along the radially extending edges of the connecting flanges in the area where the elastomer body and the connecting flanges are joined, said edges being formed are along the outer edges of the connecting flange segments, and/or on the inner edges of breakthroughs in the connecting flange, the connecting flanges axially project outwards from the plane of the connecting flange with respect to the elastomer body; and that the elastomer body is joined with the flanges along the arched area by vulcanization.
According to the invention, the connecting flanges are bent axially outwards in those locations where the free edges of the rubber/metal connection interface extend radially and are consequently exposed to special loads. This applies in particular to the inner edges of breakthroughs, i.e. of venting openings provided in the connecting flange, or, in conjunction with segmented connecting flanges, to the radial outer edges of the connecting flange segments. Owing to the outwardly projecting edge zone as defined by the invention, the area where the rubber and the metal are joined by vulcanization is widened in the axial direction beyond the axial width of the connecting flange.
For practically implementing the design as defined by the invention, it is possible also to bend the plate-like connecting flanges axially outwards along the edges, or, as an alternative, to form an axially outwards projecting bead along the edges by molding. The last-mentioned embodiment is particularly advantageous if the connecting flanges or the connecting flange segments are manufactured from cast steel.
An important advantage of the invention lies in the fact that on the one hand, the area of adhesion, i.e. the area of vulcanization within the edge zone, is enlarged irrespective of the thickness of the material of the connecting flanges in the axial direction. The force by which the rubber body is held on the connecting flange is absolutely increased, on the one hand. On the other hand, the bending stress caused by the greater radius of the curvature of the projecting or curved edges is substantially reduced vis-à-vis the relatively narrow edge zones found in the prior art, which optimizes the introduction of force into the rubber body.
Another advantageous effect of the invention is that the active elastic length of the rubber body between the edge zones projecting as defined by the invention is substantially increased, to a degree higher than it would basically be possible in the prior art. In the prior art, the rubber body theoretically can be widened only by the axial thickness of the material of the connecting flanges, whereas this limitation is overcome in conjunction with the invention because the edges of the projecting edge zones can be readily bent outwards by multiple times the amount of such axial thickness, which naturally leads to a widening within said area correspondingly. This translates into a decrease in the stress values maximally occurring during operation. In cooperation with the enlarged area of adhesion as defined by the invention and explained above, a substantial increase of the power density is achievable.
The embodiment as defined by the invention is equally applicable to the design of the radial edges of connecting flange segments as well within the breakthrough arranged in the connecting flanges. In connection with the breakthroughs, this is possible irrespectively of whether they are filled with rubber material, or whether such breakthroughs are adjoined by venting channels in the rubber body.
In a preferred embodiment of the invention, the torsion element has venting openings axially extending through the connecting flanges and the elastomer body. The interior of the elastomer body is effectively cooled by air flowing through the axial venting channels adjoining the axial breakthroughs in the connecting flange. Owing to the fact that the venting openings are arranged within breakthroughs provided as defined by the invention, i.e. provided with projecting or beaded edges, enhanced adhesion is obtained in the edge zones of the rubber/metal joint located there as well.
According to a further development of the invention, provision is made that the elastomer body has radial venting channels. This makes it possible, furthermore, that the radial venting channels can be connected with the aforementioned axial venting channels. In this way, the torsion elements are structured in the way of a radial compressor. During rotation, ambient air is aspirated via the axial openings due to centrifugal forces, and discharged into the outside by way of the radial venting channels across the periphery of the elastomer elements. The constant flow of air results in particularly effective cooling.
The radial venting channels are usefully open radially outwards. This means that they can be closed radially inwards. Active rubber material therefore remains standing in the interior for transmitting the torque.
In conjunction with embodiments having radial venting openings, it is particularly advantageous if the connecting flanges have breakthroughs located within the peripheral zone between said radial venting openings. Such breakthroughs do not change into venting channels but are filled with rubber material. By virtue of the embodiment as defined by the invention, comprising edge zones that are axially projecting outwards, the elastic length is increased within the zone of the breakthroughs, on the one hand, and additional adhesion and stability of the rubber body between the radial venting channels are made available on the other.